1. Field of the Invention
The present invention relates to a magnetic toner for use in electrophotography, electrostatic printing, magnetic recording, and the like, and particularly to a magnetic color toner for these purposes.
2. Description of the Prior Art
Electrophotography is an image forming process in which; an electrostatic latent images are formed by utilizing a photoconductor such as cadmium sulfide, polyvinylcarbazole, selenium, or zinc oxide, for instance, by affording uniform electric charge onto a photoconductive layer and subjecting the layer to image exposure; the electrostatic images thus formed are developed with a reverse-polarity charged toner; and if necessary, the toner images are transferred and fixed onto a transfer recording medium.
Electric printing, as disclosed in Japanese Patent Publication No. 14342/67 and in other literature, involves guiding an electrically charged toner powder to form toner images on a recording medium by utilizing electric field and fixing the images.
Electrostatic recording is a process in which electrostatic latent images are formed from information signals on a dielectric layer and developed with an electrically charged toner powder, and the resulting toner images are fixed.
Magnetic recording is a process in which magnetic latent images are formed similarly on a recording medium and developed with a magnetic material-containing toner powder, and the resulting toner images are transferred and fixed onto a transfer recording medium.
A variety of techniques are known to develop these electric or magnetic latent images with toners. The techniques are roughly classified into the dry development process and the wet development process. The former is further divided into a process employing a two-component developer composed of toner particles and carrier particles and a process employing a one-component developer which does not contain carrier particles.
Prevailing techniques belonging to the process employing a two-component developer are the magnetic brush process and the cascade process, which are different from each other in the type of carrier for carrying a toner, the former employing a powdered iron carrier and the latter employing a bead carrier.
There have been proposed a variety of processes which employ a one-component developer composed of a toner alone. Of these processes, many excellent processes employing a magnetic toner are in practical use, including the Magne-Dry process, which employs an electrically conductive toner; the process of DAS No, 2,704,361, which utilizes the dielectric polarization of toner particles; the process of U.S. Pat. No. 4,121,931 in which electric charge is transferred by agitation of a toner; and the processes of U.S. Ser. Nos. 938,101 and 58,434, offered by the present applicant, in which latent images are developed with toner particles flying toward them.
On the other hand, the purpose of recording or copying has been diversified recently and a color copying machine compact and inexpensive is desired which is capable of forming images of different colores according to requests. In the one-component magnetic toners mentioned above, magnetite or ferrite has been used conventionally as the magnetic material. Its color, being black or dark brown, is a great obstruction to the preparation of a so-called color toner though effective for a black toner. In order to surmount this obstruction, whitening or coloring of black magnetic materials has been proposed. However, these proposed methods are not only insufficient for masking the magnetic material and forming an image of intended color, but also unsatisfactory in various practical characteristics of the toner for performing electrophotography, including initial stage properties such as developing ability, transferability, fixability, and cleaning ability and long-term properties such as durability, environmental stability, and preservability.